1. Field of the Invention
The invention generally relates to a mil-dot reticle. In particular, the invention relates to a targeting reticle for firearms and the like, whereby a plurality of dots are and evenly-spaced hash-mark graduations between the dots are combined to form the reticle
2. Description of the Related Art
A reticle is a grid or pattern placed in either of two focal planes of an optical instrument, such as a riflescope to establish scale or position. As shown in FIG. 1, the first focal plane A is between the objective lens assembly 1 and the erector lenses 6, a location where the first image from the objective 1 is projected. This image is up side down. The objective lens assembly 1 includes, typically, two or three larger lenses forming the objective lens assembly and is mounted in the objective end 2 of the optic. It is called an objective lens because it is closest to the xe2x80x9cobjectxe2x80x9d being viewed. The erector lenses 6 turn/rotate the image in the first focal plane A 180 degrees, i.e., erecting the image. The second focal plane B is between the erector lenses 6 and the ocular assembly 7. After light rays pass through the erector lenses 6, the image is projected onto this location, where the image will be seen by the user when looking in the scope from the right end 8. The reticles in the first focal plane A are sometimes referred to as magnifying reticles because appearance changes at the same ratio as the image size. Any reticle with markers off center and installed in the first focal plane A will have the same subtension (coverage on the target, i.e., spacing and size) regardless of the power setting in a variable power scope. The user can range estimate at any power and compensate for moving target leads to suit conditions. For example decreasing power allows a larger field of view and more light transmission.
Any reticle in the second focal plane B is often referred to as a non-magnifying reticle because the appearance to the eye is the same to the eye regardless of power setting in a variable power scope. Any reticle having markers off the center of the reticle will have correct spacing at only one magnification. The scope tube or housing 3 is designed to hold the various component parts. The top adjustment 5 moves the reticle so as to zero the scope can be zeroed. A second adjustment (not shown) may be place on the side of the tube at 90 degrees to the top adjustment 5.
Even though riflescopes have become increasingly sophisticated, the basic constriction has remained the same. Light rays entering the objective lens are magnified. The resulting enlarged and upside-down image proceeds through the erector lens system, which magnifies and corrects the image to the right-side-up position. Finally, the ocular lens further magnifies and projects the target image and reticle to the user""s eye.
The reticle is positioned within the optical system to coincide with the plane of focus of the objective lens or lens group. In a variable power scope, as the spacing between the lenses changes, the magnification of the scope also changes. The total travel of the lenses is called the zoom ratio. Typically it would be a 3xc3x97 ratio. Variable power scopes have powers specified in these ratios. For example 3.5xc3x97-10xc3x97 or 2.5xc3x97-8xc3x97. Ratio is up to the manufacturer and may be anywhere between 3xc3x97 and 5xc3x97.
The reticle is commonly referred to as the xe2x80x9ccrosshair,xe2x80x9d and often consists of fine wires, dots, pointed posts or other distinct shapes that appear superimposed on the first or second focal plane. In principle, relatively bold reticles aid rapid aiming, while finer reticles subtend less of the target and may be less prominent, but are conducive to precise shot placement when aiming carefully and deliberately.
U.S. Pat. No. 6,032,374 shows a telescopic gunsight with a reticle having a primary vertical line 20, a primary horizontal line 22 intersecting the primary vertical line 20, a plurality of secondary horizontal lines 24 each having a predetermined thickness and evenly spaced a predetermined distance along the primary vertical line 20, a plurality of secondary vertical lines 26 each having a predetermined thickness and evenly spaced a predetermined distance along at least some of the secondary horizontal lines 24, and a range-finder 30 positioned in one of the quadrants formed by the intersection of the primary vertical and horizontal lines. A plurality of half hash-marks (2.5 inches of angle) are placed between the secondary horizontal lines 24. The horizontal lines are asymmetrical to the optical center 21 with fewer and shorter lines on the top. The vertical lines mirror to the primary vertical line 20 with numbers 28. The range-finder 30 is placed at the lower left quadrant. The asymmetrical arrangement in conjunction with the numerous hairs complicate the reticle and can confuse the user. A plurality of horizontal half hash-marks further distract the user. In addition, the spacing between the lines is most preferably based upon the xe2x80x9cinches of anglexe2x80x9d scale rather than the xe2x80x9cminute of anglexe2x80x9d scale or Mil Radian scale, which have been adopted by the military for years.
Radians are used in a coordinate system called xe2x80x9cpolar coordinates.xe2x80x9d The radian is a unitless measure which is equivalent, in use, to degrees. It is an angular measure equal to the angle subtended at the center of a circle by an arc equal in length to the radius of the circle, approximately 57xc2x0 17xe2x80x244.6xe2x80x30.2xcfx80 radians=360 degrees. A point on the plane is defined, in the polar coordinate system, using the radian and the radius. The radian defines the amount of rotation and the radius gives the distance from the origin (in a negative or positive direction).
Switching from the xe2x80x9cdegreexe2x80x9d mode to the xe2x80x9cradianxe2x80x9d mode, one milliradian={fraction (1/1000)} (0.001) radians in the mil-dot reticle. The mil-dot reticle, which was designed to help U.S. Marine Corps snipers estimate distances, became standard for all military branches. All mil-dot reticles in current use have 10 mils space vertical and horizontal. The mil-dot reticle does not limit the user to one size or a limited number of sizes. The mil-dot reticle is now also the standard reticle found in law enforcement riflescopes. It has been adopted over the years by sportsman and hunters as a serious aid for range estimating. The mil-dot reticle is a reliable means for determining distances to targets, establishing leads for moving targets, and for alternating aiming points for windage and elevation considerations. Military snipers who have been trained in formal instruction programs spend numerous hours honing their ability to use the mil-dot reticle so as to be comfortable and competent with it. In contrast, some civilian tactical and practical long-range precision shooters are hesitant of the mil-dot reticle because of a lack of proper training. Aids available for the proper use of the mil-dot reticle include a simple formula that can be used with a calculator, mil tables or a slide rule type calculator called the MILDOT MASTER(trademark). This calculator can be found at this link http://www.premierreticles.com/mildotmstr.htm.
The mil-dot reticle is designed around the measurement unit of the milliradian. The dots and the spacing of the dots are also designed based upon the milliradian. The space between dot centers subtends one milliradian(mil). This allows a shooter to calculate the distance to a target of a known height or width. For example, the height of the target in yards divided by the height of the target in milliradians multiplied by 1000 equals the distance to the target in yards. The height or width of the target has to be known to use this system effectively. A milliradian is an angular unit of measure that equals one yard at 1000 yards and 1 meter at 1000 meters. The distance to a target can be decided when the size of the target is known. The shooter simply measures the target using the dots, then uses a simple formula to obtain the target""s distance or the distance to an item near the target. For example, if the top of the head of a 6-foot-tall man (2 yards) is lined up with one dot and his feet are lined up four dots down, he is ({fraction (2/4)})*1000=500 yards away. The same technique can be used to estimate a lead on a moving target or to compensate for deflection on a windy day. A conversion table with xc2xd increments is available at http://www.swfa.com/mildot/, and a conversion table of xc2xc increments is available at http://www.premierreticles.com/images/milchtyds.gif. As shown in the first site, the length of a dot is xc2xc mil such that the mil estimate can be further split to the nearest xe2x85x9 mil. for a more accurate range measurement. However, no actual mil scale mark of xc2xd mil has been provided.
U.S. Pat. No. 6,196,455 shows a hand-held mil-scaled calculator apparatus and a method for using the same in the field in association with firearms. The apparatus permits the user of a high-powered rifle equipped with a telescopic sight having a mil-dot reticle to quickly determine the range to target and the necessary elevation adjustment to compensate for bullet drop. However, its hash-marks (the first embodiment in FIG. 1 and the second embodiment in FIG. 9 of the patent) are unevenly-spaced.
The size, shape and spacing of the lines and mil-dots are extremely useful for measuring the target. The website at http://www.leupold.com/products/reticles.htm lists many commercially available reticles, including mil-dot reticles with evenly-spaced round dots which are symmetric to the optical center. The mil-dot reticle pattern shown at the website http://www.swfa.com/mildot/, manufactured by the applicant Premier Reticles, Ltd., is made up of the same number of horizontal and vertical dots placed on a cross hair. They are applied wet to a fine wire and appear oval because of the surface tension of the material drawing the dots into an oval shape when added to the wire. Mil-dot reticles made from fine wire are termed xe2x80x9cmechanicalxe2x80x9d. They are xc2xc mil. long (0.86 MOA) and {fraction (7/16)} MOA narrow. The term xe2x80x9cminute-of-anglexe2x80x9d (MOA) is used regularly by target shooters (one MOA is about 1xe2x80x3 at 100 yards). If the rifle is shot 5 times into a 100-yard target and every shot went into an one-inch circle, then the rifle could be said to shoot 1 MOA. Likewise, if every shot goes into a two-inch circle at 200 yards, it shoots 1 MOA. A 10-inch group at 500 yards would be 2 MOA.
Reticles can be made with two other methods. One method is etching a reticle with a foil approximately 0.0015xe2x80x3 thick. This foil is photographed and then acid etched. The acid removes all but the remaining reticle design that was photographed. A second and more common method is a chrome-filling process to provide a glass reticle. Glass reticles are approximately 1-2 mm thick and are sized on the outside diameter to fit within the optical system. An image is photographed on the surface, acid etched and then chrome filled. It is also possible to laser mark the glass and then chrome fill the reticle pattern. Alternatively, a glass reticle is produced by applying a chrome image directly onto the glass.
The current designs of mil-dot reticles have dots that are of either the following two sizes via the above-mentioned methods. The mechanical wire mil-dot reticles prevent retro-reflection caused by the glass, while these mechanical dots applied to fine wire are always oval, such as some supplied by Leupold(copyright), http://www.swfa.com/mildot/having oval dots of xc2xc mil long (0.86 MOA). Unless a dot is installed at the intersection of two lines, it will always be oval-shaped by applying the traditional mechanical painting method. Another dot size is a round dot with a xc2xe MOA (0.22 mil) diameter, such as those offered by Leupold in some of their scopes, including the illuminated scopes and Mark 4 scopes. These designs do not allow the mil increments to be broken down into 0.1 mil increments. The xc2xc mil oval dot as shown in FIG. 2 can only be broken down into xc2xc mils but with difficulty. It would be impossible to find any 0.1 mil increments in a prior art reticle because 0.25 is not divisible by 0.1 and it would take a lot of extrapolation to estimate anything smaller than xc2xc mils.
The KLEIN reticle has 0.1 mil radius round dots and evenly-spaced hash-mark gradients placed between the dots such that the shooter can speculate the nearest 0.2 mil. The hash-mark gradient is in the KLEIN reticle are 0.4 mil which over powers the 0.2 mil diameter dots, and its post width is also 0.4 mil. The KLEIN hash marks are only 0.035 mil thick which is hard to see at lower powers, such as under 10xc3x97. In addition, the KLEIN reticle only provide bare posts.
Currently, there is a demand for a mil-dot reticle with 0.2 mil round dots and shorter evenly-spaced hash-mark gradients placed between to improve ranging accuracy, and there is also a demand for better designed posts to improve ranging efficiency.
It is a purpose of this invention to provide a mil-dot reticle to assist a shooter to produce more accurate and repeatable results.
It is another purpose of this invention to provide a plurality of mil-dots with half mil hash-marks between the dots on a reticle.
It is still another purpose of this invention to answer to persistent requests from various military and law enforcement operators for a more user friendly and accurate mil-dot reticle to be applied to variable power scopes or optical assemblies for amplifying a distance object, such as telescopes, binoculars, spotting scopes, shooting scopes, etc. The second request is to increase the versatility of the ranging capability to allow range estimating for larger objects at closer distances. The current design mil-dot reticle has up to 10 mils of space. For example a 25 foot object could be estimated from 833 yards to 8333 yards with the existing 10 mil increment mil-dot reticle. Adding 5 mil increment markers out from center greatly increases the ranging capability for larger objects. If when ranging the 25 foot object fills 50 mils the distance is 167 yards. The end result is a ranging capability from 167 yards to 8333 yards. These extra markers also allow a military forward observer to direct placement of artillery and mortar rounds.